The present invention relates to a thermal or heat-sensitive transfer material which can provide transferred recorded images of good image quality even on a recording medium with poor surface smoothness, and a thermal transfer recording method using the same.
The thermal or heat-sensitive transfer recording method has advantageous features in that it can provide recorded images on plain paper in addition to the general features of the thermal recording method, i.e., that the apparatus therefor is light in weight, compact, free of generating noise and also excellent in operability and maintenance. For these reasons, the thermal transfer recording method has been recently widely used.
The thermal transfer recording method employs a thermal transfer material, comprising generally a heat transferable ink containing a colorant dispersed in a heat-fusible binder applied on a support generally in the form of a sheet. The thermal transfer material is superposed on the recording medium so that the heat-transferable ink layer may contact the recording medium, and the ink layer, melted or softened (hereinafter simply referred to as "melted") by supplying heat by a thermal head from the support side of the thermal transfer material while supporting the back side of the recording medium, is transferred onto the recording medium, thereby forming a transferred ink image corresponding to the pattern of the heat supplied on the recording medium.
However, as the transfer is effected based on the viscosity of the ink melted on heating in the thermal transfer recording method, the transfer recording performance, namely the recorded image quality is greatly influenced by the surface smoothness of the recording medium, and therefore, although good transfer can be effected on a recording medium with high smoothness, the image quality will be markedly lowered on a recording medium with poor smoothness. For this reason, a paper having a high surface smoothness is required in order to effect good quality of image recording. However, plain paper which is the most typical recording medium possesses various degrees of concavities and convexities due to entanglement of fibers. Accordingly, in the case of a paper with a large surface unevenness, the heat-melted ink cannot penetrate into the fibers of the paper during transfer recording, but only adheres at the convexities of the surface or in the vicinity thereof, with the result that the transferred image at the edge portion is not sharp or a part of the image may be lacking to lower the image quality. For improvement of the image quality, there has been taken a measure of using a heat-fusible ink having a low melt viscosity, or increasing the thickness of the heat-transferable ink layer based on a concept of causing the melted ink to penetrate faithfully into the surface unevenness of paper, etc. However, the above measures have not been successful in improving the image quality. Further, when an ink having a low melt viscosity is used, the heat transferable ink layer will be sticky at a relatively low temperature to result in lowering in storability or troubles such as staining at non-image portions of the recording medium or blurring of transferred images. Further, in a case where a transferable ink layer having a large thickness is used, blurring becomes remarkable and a large amount of heat supply from a thermal head is required to raise the recording speed.